Temperature Classification | Hazardous Area T Class Ratings

This page on Temperature Classification | Hazardous Area T Class Ratings is an excerpt from the original Temperature Classification webpage, published on the Control And Instrumentation.com website, and is published here with their permission.

All products certified suitable for use in a hazardous area, whether they be instruments, enclosures, luminaries etc should be marked with their temperature class. The temperature class defines the maximum surface temperature the product is allowed to operate at. Temperature class is referenced to an ambient of -20°C to +40°C unless specifically indicated otherwise.
According to the types of explosion protection used on the product e.g. Exd, Exe etc, the temperature corresponds either to the maximum temperature of the external surface of the product, or to the maximum temperature of the internal surface of the product.

When selecting a product, ensure the temperature class of the product is below the minimum ignition temperature of the explosive atmosphere where it will be installed.
North American and Canadian practice differs from that used in Europe with smaller temperature ranges being allowed in the new world.

Temperature Classification
Max. Surface Temp °C	North American	European
450	T1	T1
300	T2	T2
280	T2A	---
260	T2B	---
230	T2C	---
215	T2D	---
200	T3	T3
180	T3A	---
165	T3B	---
160	T3C	---
135	T4	T4
120	T4A	---
100	T5	T5
85	T6	T6

The European codes allow for a Small Component Relaxation as below;

Surface Area	T4 Classification
< 20mm²	Surface temperature < 275°C
>20mm² <10cm²	Surface temperature <200°C
>20mm²	Power dissipation <1.3 W at 40°C ambient Power dissipation <1.2 W at 60°C ambient Power dissipation <1.0 W at 80°C ambient

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